1. Field of the Invention
The present invention relates to a high voltage output device applied to laser printers and laser multi function peripherals (MFPs). More particularly, the present invention relates to a power control apparatus and method for addressing a problem in image quality by constantly controlling an alternating current (AC) power used for developing.
2. Description of the Related Art
AC power is very important in image forming devices, such as laser beam printers (LBPs), which are a contactless developing method.
FIG. 1 is a circuit diagram of an apparatus known in the prior art for controlling electric power supplied to a developing unit.
As illustrated in FIG. 1, the prior art power control apparatus includes a pulse width modulation (PWM) input unit 10 receiving a PWM signal from an engine controller (CPU: Central Processing Unit) (not shown), a comparator 20 comparing the PWM signal to a reference signal, a switching unit 30 forming a reference comparison output signal using a voltage Vcc, and a transformer 400 transforming a switching result into a high voltage, in order to output an AC power of a high voltage. The AC power output from the transformer 400 is applied to the developing unit.
The prior art apparatus is configured to output a constant voltage in response to an input PWM signal. However, since a feedback control is not performed, deviation of an output voltage occurs according to an environment. The variation of the output voltage is caused by an environmental characteristic (temperature/humidity) of each of the components constructing the prior art circuit and the variation of a load (the developing unit) connected to a high voltage output terminal.
Thus, if the AC power supplied to the developing unit cannot output a voltage as required by a process, a problem in image quality occurs. That is, if a voltage higher or lower than the required voltage is applied to the developing unit, a problem in image quality occurs.
Accordingly, there is a need for an improved power supply apparatus and method of its use.